The present invention relates to a photographic light-sensitive material, and, more particularly, to a silver halide photographic light-sensitive material having improved antistatic properties by the presence of a specific water-soluble polymer.
The antistatic property of a material relates, in general, to surface resistivity and charge. Reduced surface resistivity and a small charge are desired and it is also requested that these properties do not deteriorate with the passage of time.
A photographic light-sensitive material generally comprises a support such as film of a poly-.alpha.-olefin (e.g., polyethylene, polystyrene, etc.), cellulose ester (e.g., cellulose triacetate, etc.), polyester (e.g., polyethylene terephthalate, etc.), paper, synthetic paper, or a paper sheet coated on both sides with polymeric materials, having coated on one side or both sides light-sensitive photographic emulsion layer (or layers) with an interposed subbing layer provided to strongly adhere the support to the photographic emulsion layers, and, if desired or necessary, various layers constituting photographic light-sensitive materials such as interlayers, protective layers, a backing layer, an antihalation layer, or the like, in various combinations.
Examples of a photographic light-sensitive material having a photographic emulsion coated on both sides of a support include, for example, X-ray film for direct use. Most other photographic light-sensitive materials are coated only on the one side with a photographic emulsion.
Therefore, the latter type of photographic materials have a photographic emulsion-free surface, i.e., the surface of the support, usually called the "backing" side. Since photographic light-sensitive materials comprise a support and photographic layers having an insulating property, electrostatic charges are liable to be generated and accumulated during the production of photographic light-sensitive materials and during use thereof due to contact friction with or delamination from the surface of the same or different substances. This accumulated electrostatic charge can cause many difficulties. For example, in the photographic film before development processing, the light-sensitive emulsion layer will respond to the discharge of the accumulated electrostatic charge to form dot-like spots or tree-like or feathery linear patterns after developing the photographic film, which spots or patterns are ordinarily called static marks. Such marks seriously deteriorate, or, in some cases, completely spoil the commercial value of photographic films. For example, it can easily be seen that static marks appearing in X-ray film for medical or industrial use could lead to extremely dangerous misdiagnosis. The existence of this phenomenon is confirmed only after development, and is therefore an extremely difficult problem. In addition, the accumulated electrostatic charge can cause adhesion of dust on the film surface, and secondary problems such as formation of non-uniform coatings or the like.
As is described above, such electrostatic charge often accumulates upon production of photographic light-sensitive materials and upon use. For example, in production, electrostatic charges are generated through contact friction between the photographic film and rollers or separation between the support surface and the emulsion-coated surface in steps involving winding of photographic films. Also, with finished products, electrostatic charges are generated by delamination of a base surface from an emulsion-coated surface when winding of the photographic film is conducted in a humidity high enough to cause film adhesion, or by the contact and delamination of X-ray film from mechanical parts in an automatic processing machine or from a fluorescent sensitizing paper. In addition, it may also be generated by contact with a wrapping material. Static marks of photographic light-sensitive materials to be formed by the accumulation of such electrostatic charge become much greater as the sensitivity of the photographic light-sensitive material is increased and as the speed of processing (processing velocity) is increased.
These frictional charges or delamination charges are considered to be caused by a mutual ionic action between the molecules of contacted substances. However, at present, it is difficult to predict from structural and chemical viewpoints what substance will be negatively charged and what substances will be positively charged.
A solution, however, is to reduce the charge voltage, or to increase electric conductance on the surface of a substance, to thereby release electrostatic charge in an extremely short time before localized discharge due to the accumulation of electric charge can occur, so as to prevent such charging and discharging. Therefore, various processes have been suggested for improving the electroconductivity of the support or various coated surface layers of photographic light-sensitive materials, and various hygroscopic substances, water-soluble inorganic salts, certain kinds of surface active agents, and polymers have been utilized. For example, polymers as described, e.g., in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, etc., surface active agents as described, e.g., in British Pat. No. 861,134, U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, etc., zinc oxide, semiconductors, colloid silica, etc., as described, e.g., in U.S. Pat. Nos. 3,062,700, 3,245,833, 3,525,621, etc., are known.
Known processes for directly imparting an antistatic property to photographic film supports include processes of directly compounding certain substances in a support of a high molecular weight material, and processes of coating such substances on the surface of the support. In the latter case, an antistatic agent is coated as a backing layer by using it alone or in combination with gelatin, polyvinyl alcohol, cellulose acetate, or a similar polymeric substance.
Also, a process is known for preventing charging of photographic light-sensitive materials by incorporating an antistatic agent in a photographic emulsion layer or a surface protecting layer thereof, or coating a solution of an antistatic agent on the surface of such layers. However, many of these show specificity depending upon the kind of film support or the composition of the photographic materials. Thus, a particular agent providing good results for certain film supports, photographic emulsion layers, or other photographic layers may be useless for antistatic purposes with respect to other different film supports and photographic layers, and, in some cases, exerts a detrimental influence on photographic properties.
In general, with high speed emulsions there are few antistatic agents which provide satisfactory antistatic effects under conditions of low humidity (about 30% relative humidity (RH)). In many cases, a reduction in antistatic effects and an increase in adhesion problems occur under conditions of high temperature and high humidity. In particular, with light-sensitive materials wherein a photographic emulsion is coated on both sides of a support (such as X-ray light-sensitive materials), it has been difficult to discover effective antistatic agents.
Further, it has been particularly difficult to establish stable antistatic properties, since in many cases antistatic properties which have been granted tend to decrease with the passage of time or due to friction.
Also, in the case of searching for antistatic agents for photographic light-sensitive materials, it is necessary to take into consideration the sensitivity, fog, granularity, sharpness, and other photographic properties, as well as the points of maintaining a suitable friction constant, and of not deteriorating camera behavior, i.e., characteristics of light-sensitive materials observed when the light-sensitive materials move within a camera, e.g., slipperiness at the time of loading or feeding films in the camera, or adhesion resistance.
For a certain compound to achieve the intended effect as an antistatic agent, it is generally required that the compound be incorporated in a photographic light-sensitive material in a greater amount than when it is used for other purposes (for example, as a coating aid, an emulsifying agent, or a sensitizing agent). This is presumably because an antistatic agent must form a continuous layer in order to remain electrically conductive in a photographic layer. However, when the antistatic agent is used in such a great amount, much of it remains on the surface of a light-sensitive material, causing various problems in the preparation or use of the light-sensitive material, since it may be transferred to transport rollers, the camera, or X-ray screen that contact the surface of the light-sensitive material. For instance, an antistatic agent transferred to a transport roll may stain the roll, and the stain may be deposited on a film that subsequently passes between the rolls. If the antistatic agent is transferred from an X-ray film to a screen, the characteristics of the screen may be changed, or a stain or blur may be formed on the X-rayed photographic material. This not only impairs the product quality, but may result in an inaccurate diagnosis. Thus, it is very difficult to apply antistatic agents to photographic light-sensitive materials, and the selection of antistatic agents is very restricted as described above.